What is a battery?

The battery, in conjunction with the alternator, supplies the electrical power needed for the lights, stereo, and all other electrical components. The battery stores electrical power to start the engine, and allows electronic components to function when the alternator cannot produce enough power.

How does the battery work?

As the engine is running, the alternator is constantly recharging the battery, and providing electrical power to the vehicle simultaneously. The battery stores this electrical power and, when requested by turning the key, uses the stored power to start the engine. When additional batteries are stored on a vehicle, they may assist in starting the engine, or they can send power to additional components that were not included with the vehicle when manufactured. Some vehicle's use up to four batteries, such as the original HUMMER, but for the overwhelming majority of vehicle's, one battery is sufficient for all standard operations.

What are the symptoms related to a bad battery?

The battery is considered “dead” when there is insufficient charge to start the engine, or run electrical components. Normally, the first sign is dim lighting in the interior of the vehicle, and when attempting to start, the engine may crank extremely slowly, or not at all. A very rapid clicking noise is normally heard if there is any charge left in the battery, but in many cases the vehicle will be completely unresponsive to any input. If the battery is losing charge while driving the vehicle, the battery warning light will illuminate, and the engine may stall from lack of electrical power needed to run.

Can I drive with a battery problem?

vehicle's with manual transmissions can be manually started by pushing the vehicle to considerable speed, and releasing the clutch quickly. If the battery is faulty, this will allow the vehicle to start using power from the alternator This method is commonly called push-starting, and is an effective method of manually starting the engine using the vehicle's transmission to turn the flywheel. The vehicle may be able to start using jumper-cables, but if the battery is faulty, the jumper-cable wire thickness must be sufficient to allow the engine to start using power exclusively from the second vehicle’s battery.

How often do batteries need to be replaced?

Batteries fail at no specific mileage interval or age. The older a battery however, the more typical it is to experience failure. Proper maintenance of the starting and charging system can prolong the life of the battery, as well as other starting and charging components.

How are battery issues diagnosed?

A "dead battery" does not necessarily mean the battery is at fault. Vehicles exhibiting the symptoms of a dead battery should be properly tested (e.g. individual cell voltage, load, and conductance tests) by connecting to a starting and charging system test machine. This is an advanced device that will test every part of the starting and charging system automatically by following onscreen instructions. The machine will display results and may also require the servicing technician to complete visual inspections while testing is in progress. If the battery is found to be discharged below the required voltage, it will be recharged, retested, and possibly replaced. If the battery is not at fault, other issues that cause electrical current flow — sometimes in very low amounts after the vehicle is shut off — can cause chronic dead battery problems and be the true cause.

Battery Replacement Cost Estimates

The average cost for a Battery Replacement is between $52 and $67 but can vary from car to car.

How is a battery replaced?

Battery replacement, for most vehicles, is typically fast and easy. When replacing the battery, battery cable, or the battery cable end, apply the emergency brake, remove the keys from the ignition, and turn off all electrical components. Before disconnecting the battery, make sure the radio anti-theft code is available; some vehicles require certain systems to be reset or "learned" after the battery is installed. These can include engine and/or transmission adaptation, power window pinch protection, power seat/mirror settings, and radio station presets.

When ready, the battery cables should be disconnected and any battery insulation material should be removed. The negative cable is always removed first, followed by the positive cable. After removing both cables, the hardware holding brackets are loosened and/or removed. If you carefully follow these steps, any reserve voltage in the electrical system will equalize. The battery will then be free for removal.

When installing the new battery, always connect the positive cable first, followed by the negative cable because the computer memory and adaptive functions will start to energize as soon as the new battery is connected. To avoid damaging the computers or software in the vehicle, it is important to have the correct polarity.

Note that some vehicles place the battery in the trunk, the front or rear wheel well, or under the seats. In these instances, accessibility of the battery may dictate dismantling several components before the replacement can begin.

OBD codes related to Battery Replacement

RepairPal Recommendations for battery issues

We recommend using a battery rated identically to the original battery. Using too small or too large of a battery will result in overcharging or undercharging, and will lead to repeated failure.

What to look out for when dealing with battery issues

A dead battery can be caused by several components. Most commonly, the issues causing battery power depletion are battery cables, failed connections due to corrosion, an electrical system malfunction causing battery drain while the vehicle is off, and long periods without using a vehicle. That being said, the battery must be tested prior to replacement, as the battery very often replaced needlessly when a jumpstart or other solution would suffice.

Can I replace the battery myself?

Replacing the battery, or batteries, is a great DIY project that can be completed in short order for most vehicle's. However, there is a risk of electrical shock and other electrical component failure if arcing occurs at the battery terminals. Prior to performing this maintenance, the vehicle's battery location should be noted and if the location requires much disassembly, either a very experienced DIYer, or a trained technician should be trusted with the repair.